1. Field of the Invention
The present invention relates to a fuel supply system for an injection-type internal combustion engine which raises a pressure of fuel applied to each fuel injector above a regulated pressure value so that the engine can be smoothly operated without occurrence of a vapor lock at the time of high fuel temperature.
2. Statement of the Prior Art
A conventional fuel supply system for an injection-type internal combustion engine comprises: PA1 (1) a fuel tank; PA1 (2) a fuel injector located at an intake port of intake manifold of each engine cylinder; PA1 (3) a fuel pump located at a fuel supply line between the fuel tank and the fuel injector for applying a pressure to the fuel fed from the fuel pump; PA1 (4) a fuel damper located at the fuel supply line from the fuel pump; PA1 (5) a fuel filter located at the fuel supply line from the fuel damper; and PA1 (6) a fuel pressure regulator which regulates the pressure of fuel to be supplied to each injector so that the difference between the fuel pressure and a vacuum pressure within the intake manifold indicates a constant value (e.g., approximately 2.55 kg/cm.sup.2) and returns an extra amount of fuel into the fuel tank via a fuel return line; and PA1 (7) a fuel injection control unit which outputs a pulse signal into an electromagnetic valve of each fuel injector, the duty ratio of the pulse signal being based on various engine operating parameter signals such as an intake air flow rate signal, an engine revolutional speed signal, and so on, so that the fuel injector injects an optimum amount of fuel into the corresponding cylinder according to the engine operating condition.
There is a problem in such a conventional fuel supply system, however, in that since the whole fuel supply system is disposed within the engine room, the fuel is heated, and particularly the fuel temperature at the fuel supply line in the vicinity of the engine body may be raised excessively so that a vapor lock of fuel occurs. This problem is especially serious when gasoline blended with alcohol is used as the fuel. Among other things in a fuel comprising of gasoline blended with 10% ethanol, a limit temperature at which the vapor lock occurs is reduced by 15.degree. C. or 16.degree. C. when compared to gasoline only fuel.
Therefore, in the case where the temperature within the engine compartment is raised when the engine is restarted minutes after the engine is stopped or during engine running at a low speed, the fuel injection control unit and fuel injectors may not operate correctly due to the clogging of the fuel supply line caused by vapor lock.